A) 6
B) 7
C) 8
D) 9
Correct Answer: C
Solution :
\[\frac{^{n}{{P}_{4}}}{^{n}{{C}_{5}}}=30\Rightarrow \frac{n\ !}{(n-4)\ !}\times \frac{5\ !\ .\ (n-5)\ !}{n\ !}=30\] \[\Rightarrow (n-4)=4\Rightarrow n=8\].
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